/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.lucene.search.suggest.document;

import java.io.IOException;
import org.apache.lucene.index.LeafReader;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.Terms;
import org.apache.lucene.search.BulkScorer;
import org.apache.lucene.search.Explanation;
import org.apache.lucene.search.Scorer;
import org.apache.lucene.search.ScorerSupplier;
import org.apache.lucene.search.Weight;
import org.apache.lucene.search.suggest.BitsProducer;
import org.apache.lucene.util.Bits;
import org.apache.lucene.util.IntsRef;
import org.apache.lucene.util.automaton.Automaton;

/**
 * Expert: the Weight for CompletionQuery, used to score and explain these queries.
 *
 * <p>Subclasses can override {@link #setNextMatch(IntsRef)}, {@link #boost()} and {@link
 * #context()} to calculate the boost and extract the context of a matched path prefix.
 *
 * @lucene.experimental
 */
public class CompletionWeight extends Weight {
  private final CompletionQuery completionQuery;
  private final Automaton automaton;

  /**
   * Creates a weight for <code>query</code> with an <code>automaton</code>, using the <code>reader
   * </code> for index stats
   */
  public CompletionWeight(final CompletionQuery query, final Automaton automaton)
      throws IOException {
    super(query);
    this.completionQuery = query;
    this.automaton = automaton;
  }

  /**
   * Returns the automaton specified by the {@link CompletionQuery}
   *
   * @return query automaton
   */
  public Automaton getAutomaton() {
    return automaton;
  }

  /**
   * Set for every partial path in the index that matched the query automaton.
   *
   * <p>Subclasses should override {@link #boost()} and {@link #context()} to return an appropriate
   * value with respect to the current pathPrefix.
   *
   * @param pathPrefix the prefix of a matched path
   */
  protected void setNextMatch(IntsRef pathPrefix) {}

  /**
   * Returns the boost of the partial path set by {@link #setNextMatch(IntsRef)}
   *
   * @return suggestion query-time boost
   */
  protected float boost() {
    return 0;
  }

  /**
   * Returns the context of the partial path set by {@link #setNextMatch(IntsRef)}
   *
   * @return suggestion context
   */
  protected CharSequence context() {
    return null;
  }

  @Override
  public ScorerSupplier scorerSupplier(LeafReaderContext context) throws IOException {
    final CompletionWeight weight = this;
    return new ScorerSupplier() {
      @Override
      public Scorer get(long leadCost) throws IOException {
        throw new UnsupportedOperationException();
      }

      @Override
      public BulkScorer bulkScorer() throws IOException {
        final LeafReader reader = context.reader();
        final Terms terms;
        final NRTSuggester suggester;
        if ((terms = reader.terms(completionQuery.getField())) == null) {
          return null;
        }
        if (terms instanceof CompletionTerms completionTerms) {
          if ((suggester = completionTerms.suggester()) == null) {
            // a segment can have a null suggester
            // i.e. no FST was built
            return null;
          }
        } else {
          throw new IllegalArgumentException(completionQuery.getField() + " is not a SuggestField");
        }

        BitsProducer filter = completionQuery.getFilter();
        Bits filteredDocs = null;
        if (filter != null) {
          filteredDocs = filter.getBits(context);
          if (filteredDocs.getClass() == Bits.MatchNoBits.class) {
            return null;
          }
        }
        return new CompletionScorer(
            weight, suggester, reader, filteredDocs, filter != null, automaton);
      }

      @Override
      public long cost() {
        throw new UnsupportedOperationException();
      }
    };
  }

  /**
   * This object can be cached
   *
   * @see org.apache.lucene.search.SegmentCacheable#isCacheable(LeafReaderContext)
   */
  @Override
  public boolean isCacheable(LeafReaderContext ctx) {
    return true;
  }

  @Override
  public Explanation explain(LeafReaderContext context, int doc) throws IOException {
    // TODO
    return null;
  }
}
